Absorbent structures with high absorbency and low basis weight

ABSTRACT

Absorbent product including a laminate of at least two plies, wherein the absorbent product has a measured Valley Volume parameter greater than 11 microns and a Pit Density of greater than 25 pockets per sq. cm.

RELATED APPLICATION

This application claims priority to and the benefit of U.S. Provisional Application No. 62/842,629, filed May 3, 2019 and entitled ABSORBENT STRUCTURES WITH HIGH ABSORBENCY AND LOW BASIS WEIGHT, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to absorbent structures, in particular to disposable paper towels or wipes, with unique surface topography that results in a product with high absorbency at lower levels of basis weight than comparable absorbent structures.

BACKGROUND

Across the globe there is great demand for disposable, absorbent structures used for household cleaning tasks. Disposable towels and wipes meet this market demand. Disposable paper towels and wipes that are composed of cellulosic based fibers are also nearly 100% renewable and biodegradable, thus catering to those whom are eco-conscience. These disposable absorbent towels and wipes are used for a multitude of tasks that require absorbency and strength. These tasks include absorbing liquid spills, cleaning windows and mirrors, scrubbing countertops and floors, scrubbing and drying dishes, washing/cleaning bathroom sinks and toilets, and even drying/cleaning hands and faces where the attribute of softness becomes important. A disposable towel or wipe that can perform these demanding tasks and be produced at a price point that provides a value proposition to the consumer is advantageous. To maintain a low price point, as well as conserve cellulosic based natural resources, providing for high strength and absorbency using the least amount of material is advantageous.

The industrial methods or technologies used to produce these absorbent structures are numerous. Absorbent structures can be produced using both Water or Air-Laid technologies. The technologies that use water to form the cellulosic (or other natural or synthetic fiber type) webs that comprises the towel or wipe are called Water-Laid Technologies. These include Through Air Drying (TAD), Uncreped Through Air Drying (UCTAD), Conventional Wet Crepe (CWC), Conventional Dry Crepe (CDC), ATMOS, NTT, ETAD, and QRT. Technologies that use air to form the webs that comprise the towel or wipe are called Air-Laid Technologies. To enhance the strength and absorbency of these towels and wipes, more than one layer of web (or ply) can be laminated together using strictly a mechanical process or preferably a mechanical process that utilizes an adhesive.

The Water-Laid technologies of Conventional Dry and Wet Crepe are the predominant method to make these structures. These methods comprise forming a nascent web in a forming structure, transferring the web to a dewatering felt where it is pressed to remove moisture, and adhering the web to a Yankee Dryer. The web is then dried and creped from the Yankee Dryer and reeled. When creped at a solids content of less than 90%, the process is referred to as Conventional Wet Crepe. When creped at a solids content of greater than 90%, the process is referred to as Conventional Dry Crepe. These processes can be further understood by reviewing Yankee Dryer and Drying, A TAPPI PRESS Anthology, pg 215-219, which is herein incorporated by reference. These methods are well understood and easy to operate at high speeds and production rates. Energy consumption per ton is low since nearly half of the water removed from the web is through drainage and mechanical pressing. Unfortunately, the sheet pressing also compacts the web, which lowers web thickness and resulting absorbency. A more detailed description of the Conventional Dry Crepe process follows.

The major steps of the conventional dry crepe process involve stock preparation, forming, pressing, drying, creping, calendering (optional), and reeling the web.

The first step of stock preparation involves selection, blending, mixing, and preparation of the proper ratio of wood, plant, or synthetic fibers along with chemistry and fillers that are needed in the specific tissue grade. This mixture is diluted to over 99% water in order to allow for even fiber formation when deposited from the machine headbox into the forming section. There are many types of forming sections used in conventional papermaking (inclined suction breast roll, twin wire C-wrap, twin wire S-wrap, suction forming roll, and Crescent formers) but all are designed to retain the fiber, chemical, and filler recipe while allowing the water to drain from the web. In order to accomplish this, fabrics are utilized.

After web formation and drainage (to around 35% solids) in the forming section (assisted by centripetal force around the forming roll, and vacuum boxes in several former types), the web is transferred to a press fabric upon which the web is pressed between a rubber or polyurethane covered suction pressure roll and Yankee dryer. The press fabric is a permeable fabric designed to uptake water from the web as the web is pressed in the press section. The press fabric is composed of large monofilaments or multi-filamentous yarns, needled with fine synthetic batt fibers to form a smooth surface for even web pressing against the Yankee dryer. Removing water via pressing results in low energy consumption.

After pressing the sheet between a suction pressure roll and a steam heated cylinder (referred to as a Yankee dryer), the web is dried from up to 50% solids to up to 99% solids using the steam heated cylinder and hot air impingement from an air system (air cap or hood) installed over the steam cylinder. The sheet is then creped from the steam cylinder using a steel or ceramic doctor blade. This is a critical step in the conventional dry crepe process. The creping process greatly affects softness as the surface topography is dominated by the number and coarseness of the crepe bars (finer crepe is much smoother than coarse crepe). Some thickness and flexibility is also generated during the creping process. If the process is a wet crepe process, the web must be conveyed between dryer fabrics through steam heated after-dryer cans to dry the web to the required finished moisture content. After creping, the web is optionally calendered and reeled into a parent roll and ready for the converting process.

The absorbency of a conventional tissue web is low due to the web being pressed. This results in a low bulk, low void volume web where there is little space for water to be absorbed. Additionally, bulk generated by crepeing is lost when the web is wetted, further reducing bulk and void volume.

The through air drying (TAD) process is another manufacturing method for making a tissue web. The major steps of the through air drying process are stock preparation, forming, imprinting, thermal pre-drying, drying, creping, calendering (optional), and reeling the web. The stock preparation and forming steps are similar to conventional dry creping.

Rather than pressing and compacting the web, as is performed in conventional dry crepe, the web in the TAD process undergoes the steps of imprinting and thermal pre-drying. Imprinting is a step in the process where the web is transferred from a forming fabric to a structured fabric (or imprinting fabric) and subsequently pulled into the structured fabric using vacuum (referred to as imprinting or molding). This step imprints the weave pattern (or knuckle pattern) of the structured fabric into the web. This imprinting step has a tremendous effect on the softness of the web, both affecting smoothness and the bulk structure. The design parameters of the structured fabric (weave pattern, mesh, count, warp and weft monofilament diameters, caliper, air permeability, and optional over-laid polymer) are, therefore, important to the development of web softness. The manufacturing method of an imprinting/structuring fabric is similar to a forming fabric (see U.S. Pat. Nos. 3,473,576; 3,573,164; 3,905,863; 3,974,025; and 4,191,609 for examples) except for an additional step if an overlaid polymer is utilized. These types of fabrics are disclosed in, for example, U.S. Pat. Nos. 6,120,642 5,679,222; 4,514,345; 5,334,289; 4,528,239; and 4,637,859. Essentially, fabrics produced using these methods result in a fabric with a patterned resin applied over a woven substrate. The benefit is that resulting patterns are not limited by a woven structure and can be created in any desired shape to enable a higher level of control of the web structure and topography that dictate web quality properties.

After imprinting, the web is thermally pre-dried by moving hot air through the web while it is conveyed on the structured fabric. Thermal pre-drying can be used to dry the web to over 90% solids before it is transferred to a steam heated cylinder. The web is then transferred from the structured fabric to the steam heated cylinder though a very low intensity nip (up to 10 times less than a conventional press nip) between a solid pressure roll and the steam heated cylinder. The only portions of the web that are pressed between the pressure roll and steam cylinder rest on knuckles of the structured fabric, thereby protecting most of the web from the light compaction that occurs in this nip. The steam cylinder and an optional air cap system, for impinging hot air, then dry the sheet to up to 99% solids during the drying stage before creping occurs. The creping step of the process again only affects the knuckle sections of the web that are in contact with the steam cylinder surface. Due to only the knuckles of the web being creped, along with the dominant surface topography being generated by the structured fabric, and the higher thickness of the TAD web, the creping process has much smaller effect on overall softness as compared to conventional dry crepe. After creping, the web is optionally calendered and reeled into a parent roll and ready for the converting process. Some TAD machines utilize fabrics (similar to dryer fabrics) to support the sheet from the crepe blade to the reel drum to aid in sheet stability and productivity. Creped through air dried products are disclosed in, for example, U.S. Pat. Nos. 3,994,771; 4,102,737; 4,529,480; and 5,510,002.

The TAD process is generally higher in capital costs than a conventional tissue machine due to the amount of air handling equipment needed for the TAD section with higher energy consumption from burning natural gas or other fuels for thermal pre-drying. The bulk softness and absorbency is superior to conventional paper due to the superior bulk generation via structured fabrics which creates a low density, high void volume web that retains its bulk when wetted. The surface smoothness of a TAD web can approach that of a conventional tissue web. The productivity of a TAD machine is less than that of a conventional tissue machine due to the complexity of the process and especially the difficulty in providing a robust and stable coating package on the Yankee dryer needed for transfer and creping of a delicate pre-dried web.

A variation of the TAD process where the sheet is not creped, but rather dried to up to 99% using thermal drying and blown off the structured fabric (using air) to be optionally calendered and reeled also exits. This process is called UCTAD or un-creped through air drying process. An uncreped through air dried product is disclosed in U.S. Pat. No. 5,607,551.

A new process/method and paper machine system for producing tissue has been developed by the Voith company and is being marketed under the name ATMOS. The process/method and paper machine system have several patented variations, but all involve the use of a structured fabric in conjunction with a belt press. The major steps of the ATMOS process and its variations are stock preparation, forming, imprinting, pressing (using a belt press), creping, calendering (optional), and reeling the web.

The stock preparation step is the same as that used in a conventional or TAD machine. The purpose is to prepare the proper recipe of fibers, chemical polymers, and additives that are necessary for the grade of tissue being produced, and diluting this slurry to allow for proper web formation when deposited out of the machine headbox (single, double, or triple layered) to the forming surface. The forming process can utilize a twin wire former (as described in U.S. Pat. No. 7,744,726) a Crescent Former with a suction Forming Roll (as described in U.S. Pat. No. 6,821,391), or preferably a Crescent Former (as described in U.S. Pat. No. 7,387,706). The preferred former is provided a slurry from the headbox to a nip formed by a structured fabric (inner position/in contact with the forming roll) and forming fabric (outer position). The fibers from the slurry are predominately collected in the valleys (or pockets, pillows) of the structured fabric and the web is dewatered through the forming fabric. This method for forming the web results in a unique bulk structure and surface topography as described in U.S. Pat. No. 7,387,706 (FIG. 1 through FIG. 11). The fabrics separate after the forming roll with the web staying in contact with the structured fabric. At this stage, the web is already imprinted by the structured fabric, but utilization of a vacuum box on the inside of the structured fabric can facilitate further fiber penetration into the structured fabric and a deeper imprint.

The web is now transported on the structured fabric to a belt press. The belt press can have multiple configurations. The first patented belt press configurations used in conjunction with a structured fabric can be viewed in U.S. Pat. No. 7,351,307 (FIG. 13), where the web is pressed against a dewatering fabric across a vacuum roll by an extended nip belt press. The press dewaters the web while protecting the areas of the sheet within the structured fabric valleys from compaction. Moisture is pressed out of the web, through the dewatering fabric, and into the vacuum roll. The press belt is permeable and allows for air to pass through the belt, web, and dewatering fabric, and into the vacuum roll, thereby enhancing the moisture removal. Since both the belt and dewatering fabric are permeable, a hot air hood can be placed inside of the belt press to further enhance moisture removal as shown in FIG. 14 of U.S. Pat. No. 7,351,307. Alternately, the belt press can have a pressing device arranged within the belt which includes several press shoes, with individual actuators to control cross direction moisture profile (see FIG. 28 of U.S. Pat. No. 7,951,269 or 8,118,979 or FIG. 20 of U.S. Pat. No. 8,440,055) or a press roll (see FIG. 29 of U.S. Pat. No. 7,951,269 or 8,118,979 or FIG. 21 of U.S. Pat. No. 8,440,055). The preferred arrangement of the belt press has the web pressed against a permeable dewatering fabric across a vacuum roll by a permeable extended nip belt press. Inside the belt press is a hot air hood that includes a steam shower to enhance moisture removal. The hot air hood apparatus over the belt press can be made more energy efficient by reusing a portion of heated exhaust air from the Yankee air cap or recirculating a portion of the exhaust air from the hot air apparatus itself (see U.S. Pat. No. 8,196,314). Further embodiments of the drying system composed of the hot air apparatus and steam shower in the belt press section are described in U.S. Pat. Nos. 8,402,673, 8,435,384 and 8,544,184.

After the belt press is a second press to nip the web between the structured fabric and dewatering felt by one hard and one soft roll. The press roll under the dewatering fabric can be supplied with vacuum to further assist water removal. This preferred belt press arrangement is described in U.S. Pat. Nos. 8,382,956, and 8,580,083, with FIG. 1 showing the arrangement. Rather than sending the web through a second press after the belt press, the web can travel through a boost dryer (FIG. 15 of U.S. Pat. No. 7,387,706 or 7,351,307), a high pressure through air dryer (FIG. 16 of U.S. Pat. No. 7,387,706 or 7,351,307), a two pass high pressure through air dryer (FIG. 17 of U.S. Pat. No. 7,387,706 or 7,351,307) or a vacuum box with hot air supply hood (FIG. 2 of U.S. Pat. No. 7,476,293). U.S. Pat. Nos. 7,510,631, 7,686,923, 7,931,781 8,075,739, and 8,092,652 further describe methods and systems for using a belt press and structured fabric to make tissue products each having variations in fabric designs, nip pressures, dwell times, etc. and are mentioned here for reference. A wire turning roll can also be utilized with vacuum before the sheet is transferred to a steam heated cylinder via a pressure roll nip (see FIG. 2a of U.S. Pat. No. 7,476,293).

The sheet is now transferred to a steam heated cylinder via a press element. The press element can be a through drilled (bored) pressure roll (FIG. 8 of U.S. Pat. No. 8,303,773), a through drilled (bored) and blind drilled (blind bored) pressure roll (FIG. 9 of U.S. Pat. No. 8,303,773), or a shoe press (see U.S. Pat. No. 7,905,989). After the web leaves this press element to the steam heated cylinder, the % solids are in the range of 40-50% solids. The steam heated cylinder is coated with chemistry to aid in sticking the sheet to the cylinder at the press element nip and to also aid in removal of the sheet at the doctor blade. The sheet is dried to up to 99% solids by the steam heated cylinder and installed hot air impingement hood over the cylinder. This drying process, the coating of the cylinder with chemistry, and the removal of the web with doctoring is explained in U.S. Pat. Nos. 7,582,187 and 7,905,989. The doctoring of the sheet off the Yankee, creping, is similar to that of TAD with only the knuckle sections of the web being creped. Thus, the dominant surface topography is generated by the structured fabric, with the creping process having a much smaller effect on overall softness as compared to conventional dry crepe. The web is then calendered (optional,) slit, and reeled and ready for the converting process.

The ATMOS process has capital costs between that of a conventional tissue machine and TAD machine. It has more fabrics and a more complex drying system compared to a conventional machine, but less equipment than a TAD machine. The energy costs are also between that of a conventional and TAD machine due to the energy efficient hot air hood and belt press. The productivity of the ATMOS machine has been limited due to the ability of the novel belt press and hood to dewater the web and poor web transfer to the Yankee dryer, likely driven by poor supported coating packages, the inability of the process to utilize structured fabric release chemistry, and the inability to utilize overlaid fabrics to increase web contact area to the dryer. Poor adhesion of the web to the Yankee dryer has resulted in poor creping and stretch development which contributes to sheet handling issues in the reel section. The result is that the production of an ATMOS machine is currently below that of a conventional and TAD machine. The bulk softness and absorbency is superior to conventional, but lower than a TAD web since some compaction of the sheet occurs within the belt press, especially areas of the web not protected within the pockets of the fabric. Also, bulk is limited since there is no speed differential to help drive the web into the structured fabric as exists on a TAD machine. This severely limits the ability to produce a bulky, absorbent paper towel. The surface smoothness of an ATMOS web is between that of a TAD web and conventional web primarily due to the current limitation on use of overlaid structured fabrics.

The ATMOS manufacturing technique is often described as a hybrid technology because it utilizes a structured fabric like the TAD process, but also utilizes energy efficient means to dewater the sheet like the Conventional Dry Crepe process. Other manufacturing techniques which employ the use of a structured fabric along with an energy efficient dewatering process are the ETAD process and NTT process.

The ETAD process and products can be viewed in U.S. Pat. Nos. 7,339,378, 7,442,278, and 7,494,563. This process can utilize any type of former such as a Twin Wire Former or Crescent Former. After formation and initial drainage in the forming section, the web is transferred to a press fabric where it is conveyed across a suction vacuum roll for water removal, increasing web solids up to 25%. Then the web travels into a nip formed by a shoe press and backing/transfer roll for further water removal, increasing web solids up to 50%. At this nip, the web is transferred onto the transfer roll and then onto a structured fabric via a nip formed by the transfer roll and a creping roll. At this transfer point, speed differential can be utilized to facilitate fiber penetration into the structured fabric and build web caliper. The web then travels across a molding box to further enhance fiber penetration if needed. The web is then transferred to a Yankee dryer where it can be optionally dried with a hot air impingement hood, creped, calendared, and reeled.

The ETAD process to date has been reported to have severe productivity, quality, and cost problems. Poor energy efficiency has been reported, bulk has been difficult to generate (likely due to high web dryness at the point of transfer to the structured fabric), and softness has been poor (coarse fabrics have been utilized to generate target bulk, thereby decreasing surface smoothness). Absorbency is better than ATMOS due to the ability to utilize speed differential to build higher bulk, but it is still below that of TAD which can create higher bulk with limited web compaction that would otherwise reduce void volume and thus absorbency. The installed costs of an ETAD machine are likely close to that of a TAD machine due to the large amount of fabrics and necessary supporting equipment.

The NTT process and products can be viewed in international patent application publication WO 2009/061079 A1, and U.S. Patent Application Publication Nos. US 2011/0180223 A1 and US 2010/0065234 A1. The process has several embodiments, but the key step is the pressing of the web in a nip formed between a structured fabric and press felt. The web contacting surface of the structured fabric is a non-woven material with a three dimensional structured surface comprised of elevations and depressions of a predetermined size and depth. As the web is passed through this nip, the web is formed into the depression of the structured fabric since the press fabric is flexible and will reach down into all of the depressions during the pressing process. When the felt reaches the bottom of the depression, hydraulic force is built up which forces water from the web and into the press felt. To limit compaction of the web, the press rolls will have a long nip width which can be accomplished if one of the rolls is a shoe press. After pressing, the web travels with the structured fabric to a nip with the Yankee dryer, where the sheet is optionally dried with a hot air impingement hood, creped, calendared, and reeled.

The NTT process has low capital costs, equal or slightly higher than a conventional tissue machine. It has high production rates (equal or slightly less than a conventional machine) due to the simplicity of design, the high degree of dewatering of the web at the shoe press, and the novelty of construction of the structured fabric. The structured fabric, which will be described later in this document, provides a smooth surface with high contact area to the dryer for efficient web transfer. This high contact area and smooth surface makes the Yankee coating package much easier to manage and creates conditions beneficial for fine creping, resulting in good sheet handling in the reel section. The bulk softness of the NTT web is not equal to the ATMOS sheet as the web is highly compacted inside the structured fabric by the press felt compared to the ATMOS web. The surface smoothness is better than an ATMOS web due to the structured fabric design providing for better creping conditions. The NTT process also does not have a speed differential into the structured fabric so the bulk and absorbency remains below the potential of the TAD and ETAD processes.

The QRT process is disclosed in US 2008/0156450 A1 and U.S. Pat. No. 7,811,418. The process can utilize a twin wire former to form the web which is then transferred to a press fabric or directly formed onto a press fabric using an inverted Crescent former. The web can be dewatered across a suction turning roll in the press section before being pressed in an extended nip between the press fabric and a plain transfer belt. A rush transfer nip is utilized to transfer the web to a structured fabric in order to build bulk and mold the web before the web is transferred to the Yankee dryer and creped. This process alleviates the NTT design deficiency which lacks a rush transfer or speed differential to force the web into the structured fabric to build bulk. However, the costs, complexity, and likely productivity will be negatively affected.

Absorbent structures are also made using the Air-Laid process. This process spreads the cellulosic, or other natural or synthetic fibers, in an air stream that is directed onto a moving belt. These fibers collect together to form a web that can be thermally bonded or spray bonded with resin and cured. Compared to Wet-Laid, the web is thicker, softer, more absorbent and also stronger. It is known for having a textile-like surface and drape. Spun-Laid is a variation of the Air-Laid process, which produces the web in one continuous process where plastic fibers (polyester or polypropylene) are spun (melted, extruded, and blown) and then directly spread into a web in one continuous process. This technique has gained popularity as it can generate faster belt speeds and reduce costs.

To further enhance the strength of the absorbent structure, more than one layer of web (or ply) can be laminated together using strictly a mechanical process or preferably a mechanical process that utilizes an adhesive. It is generally understood that a multi-ply structure can have an absorbent capacity greater than the sum of the absorbent capacities of the individual single plies. Without being bound by theory, it is thought this difference is due to the inter-ply storage space created by the addition of an extra ply. When producing multi-ply absorbent structures, it is important that the plies are bonded together in a manner that will hold up when subjected to the forces encountered when the structure is used by the consumer. Scrubbing tasks such as cleaning countertops, dishes, and windows all impart forces upon the structure which can cause the structure to rupture and tear. When the bonding between plies fails, the plies move against each other, thereby imparting frictional forces at the ply interface. This frictional force at the ply interface can induce failure (rupture or tearing) of the structure, thus reducing the overall effectiveness of the product to perform scrubbing and cleaning tasks.

There are many methods used to join or laminate multiple plies of an absorbent structure to produce a multi-ply absorbent structure. One method commonly used is embossing. Embossing is typically performed by one of three processes: tip to tip (or knob to knob), nested, or rubber to steel DEKO embossing. Tip to tip embossing is illustrated by commonly assigned U.S. Pat. No. 3,414,459, while nested embossing process is illustrated in U.S. Pat. No. 3,556,907. Rubber to steel DEKO embossing comprises a steel roll with embossing tips opposed to a pressure roll, sometimes referred to as a backside impression roll, having an elastomeric roll cover wherein the two rolls are axially parallel and juxtaposed to form a nip where the embossing tips of the emboss roll mesh with the elastomeric roll cover of the opposing roll through which one sheet passes and a second unembossed sheet is laminated to the embossed sheet using a marrying roll nipped to the steel embossing roll. In an exemplary rubber to steel embossing process, an adhesive applicator roll may be aligned in an axially parallel arrangement with the patterned embossing roll, such that the adhesive applicator roll is upstream of the nip formed between the emboss and pressure roll. The adhesive applicator roll transfers adhesive to the embossed web on the embossing roll at the crests of the embossing knobs. The crests of the embossing knobs typically do not touch the perimeter of the opposing idler roll at the nip formed therebetween, necessitating the addition of a marrying roll to apply pressure for lamination.

Other attempts to laminate absorbent structure webs include bonding the plies at junction lines wherein the lines include individual pressure spot bonds. The spot bonds are formed using thermoplastic low viscosity liquid such as melted wax, paraffin, or hot melt adhesive, as described in U.S. Pat. No. 4,770,920. Another method laminates webs of absorbent structure by thermally bonding the webs together using polypropylene melt blown fibers as described in U.S. Pat. No. 4,885,202. Other methods use meltblown adhesive applied to one face of an absorbent structure web in a spiral pattern, a stripe pattern, or a random pattern before pressing the web against the face of a second absorbent structure as described in U.S. Pat. Nos. 3,911,173, 4,098,632, 4,949,688, 4,891249, 4,996,091 and 5,143,776.

The technologies described above enable the production of absorbent structures with various attributes. With these technologies, higher absorbency is generally tied to higher basis weight (more cellulose fibers in the product). There is a continuing need for improved absorbent structures that are cost effective and more absorbent.

SUMMARY OF THE INVENTION

An object of this invention is to provide absorbent structures with previously unattainable levels of absorbency at low levels of basis weight.

An absorbent structure according to an exemplary embodiment of the present invention includes a laminate of at least two plies, wherein the absorbent structure has a measured Valley Volume parameter greater than 11 microns and a Pit Density of greater than 25.

An absorbent product according to an exemplary embodiment of the present invention includes a laminate of at least two plies, wherein the absorbent product has an absorbency of greater than 16.0 grams of water per gram of fiber and a basis weight of less than 43 grams per square meter.

Obtaining high levels of absorbency at low levels of basis weight allows for costs to be controlled by limiting the addition of costly fibrous material to the product. Environmental benefits are also obtained through conservation of natural resources that are needed to obtain fibrous material.

An absorbent product according to an exemplary embodiment of the present invention comprises a laminate of at least two plies, and the absorbent product has a measured Valley Volume parameter greater than 11 microns and a Pit Density of greater than 25 pockets per sq. cm.

According to an exemplary embodiment, the absorbent product has an absorbency of greater than 16.0 grams of water absorbed per gram of absorbent product.

According to an exemplary embodiment, the absorbent product has a basis weight of less than 43 grams per square meter.

According to an exemplary embodiment, the absorbent product is produced using a wet laid structured tissue process.

According to an exemplary embodiment, at least one of the at least two plies comprises cellulosic-based fibers.

According to an exemplary embodiment, the cellulosic-based fibers are selected from the group consisting of wood pulp, cannabis, cotton, regenerated or spun cellulose, jute, flax, ramie, bagasse, kenaf fibers and combinations thereof.

According to an exemplary embodiment, at least one of the at least two plies comprises synthetic fibers.

According to an exemplary embodiment, the synthetic fibers are made from a polymer selected from the group consisting of polyolefin, polyester, polypropylene and polylactic acid.

According to an exemplary embodiment, at least one of the two plies comprises synthetic fibers.

According to an exemplary embodiment, the synthetic fibers are made from a polymer selected from the group consisting of polyolefin, polyester, polypropylene and polylactic acid.

According to an exemplary embodiment, the absorbent product comprises both synthetic and cellulosic based polymers.

According to an exemplary embodiment, each of the at least two plies is embossed and the at least two plies are adhered together.

According to an exemplary embodiment, the at least two plies are adhered together with a water soluble adhesive mixture comprised of polyvinyl alcohol, polyvinyl acetate, starch based resins or mixtures thereof.

According to an exemplary embodiment, the water soluble adhesive is applied to at least one ply of the at least two plies at a temperature within a range of 32 degrees C. to 66 degrees C.

According to an exemplary embodiment, the water soluble adhesive mixture further comprises a water soluble cationic resin selected from the group consisting of polyamide-epichlorohydrin resins, glyoxalated polyacrylamide resins, polyethyleneimine resins, polyethylenimine resins, and mixtures thereof.

According to an exemplary embodiment, each of the at least two plies comprises an embossed area, wherein the embossed area occupies between approximately 5 to 15% of the total surface area of a surface of the ply.

According to an exemplary embodiment, each of the at least two plies comprises an embossed area having a surface, wherein a depth of embossment of the surface is between approximately 0.28 and 0.43 centimeters.

According to an exemplary embodiment, each of the at least two plies comprises an embossed area having a surface, wherein each embossment of the surface is between approximately 0.04 and 0.08 square centimeters in size.

According to an exemplary embodiment, the absorbent product is one of a paper towel, a disposable towel or wipe, a bath or facial tissue, or a nonwoven product.

According to an exemplary embodiment, the absorbent product has an absorbency of greater than 18.0 grams of water absorbed per gram of absorbent product.

According to an exemplary embodiment, the absorbent product has a basis weight of less than 40 grams per square meter.

According to an exemplary embodiment, the absorbent product has a basis weight of less than 51 grams per square meter.

A two-ply disposable towel according to an exemplary embodiment of the present invention has an absorbency greater than 18.0 grams of water absorbed per gram of towel.

An absorbent product according to an exemplary embodiment of the present invention comprises a laminate of at least two plies, wherein the absorbent product has an absorbency of greater than 16.0 grams of water absorbed per gram of absorbent product and a basis weight of less than 43 grams per square meter.

According to an exemplary embodiment, the absorbent product is a paper towel.

According to an exemplary embodiment, the absorbent product is tissue paper.

A through-air-dried disposable towel product according to an exemplary embodiment of the present invention comprises a laminate of at least two plies, and the product has a measured Valley Volume parameter greater than 11 microns and a Pit Density of greater than 25 pockets per sq. cm.

According to an exemplary embodiment, the disposable towel product has an absorbency of greater than 16.0 grams of water absorbed per gram of product.

According to an exemplary embodiment, the disposable towel product has a basis weight of less than 43 grams per square meter.

According to an exemplary embodiment, the disposable towel product is produced using a wet laid structured tissue process.

According to an exemplary embodiment, at least one of the at least two plies comprises cellulosic-based fibers.

A disposable towel product according to an exemplary embodiment of the present invention comprises a laminate of at least two plies, wherein the product has a measured Valley Volume parameter greater than 11 microns and a Pit Density of greater than 25 pockets per sq.cm, and wherein the disposable towel is through-air-dried.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and related objects, features and advantages of the present invention, will be more fully understood by reference to the following detailed description of the exemplary embodiments of the present invention, when taken in conjunction with the following exemplary figures, wherein:

FIG. 1 is a block diagram illustrating a papermaking process according to an exemplary embodiment of the present invention;

FIG. 2 is a micrograph of a structuring fabric according to an exemplary embodiment of the present invention;

FIG. 3 is a representative diagram of a creping stage of a conventional papermaking process;

FIG. 4 is a representative diagram of a creping stage of a papermaking process according to an exemplary embodiment of the present invention.

FIG. 5 is a representative diagram of an apparatus for manufacturing a laminate of two plies of a structured paper towel or tissue that are joined to each other, in a face-to-face relationship, in accordance with an exemplary embodiment of the present invention;

FIG. 6 are various diagrams illustrating calculation of Valley Volume in a sample's 3D data set through the use of its material ratio curve;

FIG. 7 are various diagrams illustrating calculation of Pit Density;

FIG. 8 shows the Pre-processing settings used to calculate Valley Volume and Pit Density in accordance with exemplary embodiment of the present invention.

FIG. 9 shows the Geometry Settings used to calculate Valley Volume and Density in accordance with exemplary embodiments of the present invention;

FIG. 10 shows the Filtering settings used to calculate Valley Volume and Pit Density in accordance with exemplary embodiments of the present invention;

FIG. 11 is a micrograph of a surface of a paper towel product made in accordance with an exemplary embodiment of the present invention;

FIG. 12 is a table providing values for various surface parameters and physical properties of a Comparative Example and various commercially available disposable towel products as compared to those of a product made in accordance with an exemplary embodiment of the present invention; and

FIG. 13 illustrates a pattern of embossments formed on the surface of a paper towel product made in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

A laminate according to an exemplary embodiment of the present invention is composed of two or more webs/plies of absorbent structures laminated together in a face-to face relationship using a heated aqueous adhesive. The laminate exhibits previously unattainable levels of high absorbency at particularly low basis weights. Each ply or a single ply may have a plurality of embossments protruding outwardly from the plane of the ply towards the adjacent ply. The adjacent ply likewise may have opposing protuberances protruding towards the first ply. If a three ply product is produced, the central ply may have embossments extending outwardly in both directions.

The absorbent structures can be manufactured by any Wet-Laid or Air-Laid methods. The materials used to produce the disposable structured tissue or paper towel product can be fibers selected from cellulosic-based fibers, such as wood pulps (softwood gymnosperms or hardwood angiosperms), cannabis, cotton, regenerated or spun cellulose, jute, flax, ramie, bagasse, kenaf, or other plant based cellulosic fiber sources in any ratio. Synthetic fibers, such as a polyolefin (e.g., polypropylene), polyester, or polylactic acid can also be used. Each ply of a multi-ply absorbent product of the present invention may comprise cellulosic based fibers and/or synthetic fibers. Also, any of the plies may be layered with a different fiber composition in each layer. Such a layering of fibers can be produced using a multilayered headbox on a wet laid asset such as a TAD paper machine.

FIG. 1 is a block diagram of a system for manufacturing a three-layered ply of an absorbent structure generally designated by reference number 100, according to an exemplary embodiment of the present invention. The system 100 includes a first exterior layer fan pump 102, a core layer fan pump 104, a second exterior layer fan pump 106, a headbox 108, a forming section 110, a drying section 112 and a calender section 114. The first and second exterior layer fan pumps 102, 106 deliver the pulp mixes of the first and second external layers 2, 4 to the headbox 108, and the core layer fan pump 104 delivers the pulp mix of the core layer 3 to the headbox 108. As is known in the art, the headbox delivers a wet web of pulp onto a forming wire within the forming section 110. The wet web is then laid on the forming wire with the core layer 3 disposed between the first and second external layers 2, 4.

Wet end additives may be mixed with the pulp prior to delivery to the headbox. To impart wet strength to the absorbent structure in the wet laid process, typically a cationic strength component is added to the furnish during stock preparation. The cationic strength component can include any polyethyleneimine, polyethylenimine, polyaminoamide-epihalohydrin (preferably epichlorohydrin), polyamine-epichlorohydrin, polyamide, or polyvinylamide wet strength resin. Useful cationic thermosetting polyaminoamide-epihalohydrin and polyamine-epichlorohydrin resins are disclosed in U.S. Pat. Nos. 2,926,154, 3,049,469, 3,058,873, 3,066,066, 3,125,552, 3,186,900, 3,197,427, 3,224,986, 3,224,990, 3,227,615, 3,240,664, 3,813,362, 3,778,339, 3,733,290, 3,227,671, 3,239,491, 3,240,761, 3,248,280, 3,250,664, 3,311,594, 3,329,657, 3,332,834, 3,332,901, 3,352,833, 3,248,280, 3,442,754, 3,459,697, 3,483,077, 3,609,126, 4,714,736, 3,058,873, 2,926,154, 3,855,158, 3,877,510, 4,515,657, 4,537,657, 4,501,862, 4,147,586, 4,129,528 5,082,527, 5,239,047, 5,318,669, 5,502,091, 5,525,664, 5,614,597, 5,633,300, 5,656,699, 5,674,358, 5,904,808, 5,972,691, 6,179,962, 6,355,137, 6,376,578, 6,429,253, 7,175,740, and 7,291,695 all of which are herein incorporated by reference.

To impart capacity of the cationic strength resins it is well known in the art to add water soluble carboxyl containing polymers to the furnish in conjunction with the cationic resin. Suitable carboxyl containing polymers include carboxymethylcellulose (CMC) as disclosed in U.S. Pat. Nos. 3,058,873, 3,049,469 and 3,998,690. Anionic polyacrylamide (APAM) polymers are an alternative to using carboxyl containing polymers to improve wet strength development in conjunction with cationic strength resins as disclosed in U.S. Pat. Nos. 3,049,469 and 6,939,443. If APAM is utilized rather than CMC, then cellulase enzymes can be utilized to build strength without concern that the enzymes would react with the CMC to cleave bonds and shorten the degree of polymerization of the molecule rendering it much less effective. The three types of cellulase enzymes that could be utilized include endo-cellulases, exo-cellulases, and cellobiase cellulases.

To impart dry strength, polymers belonging to any one of the following three categories can be mixed in the furnish separately or in combinations thereof: (i) polymers capable of only forming hydrogen bonds to cellulose fibers such as starch or certain polyacrylamides, (ii) polymers capable of additionally forming ionic bonds to cellulose fibers such as higher cationic polyvinylamines or (iii) polymers capable of covalently bonding to the cellulose fibers such as glyoxylated polyacrylamide. The polymers can be synthetic or natural. The polymers can be cationic, anionic, or amphoteric. The polymers can be copolymers, and may have linear or branched structures. In addition to amphoteric starch, suitable dry strength additives may include, but are not limited to starch and starch derivatives, glyoxalated polyacrylamide, carboxy methyl cellulose, guar gum, locust bean gum, cationic polyacrylamide, polyvinyl alcohol, anionic polyacrylamide, styrene-butadiene copolymers, vinyl acetate polymers, ethylene-vinyl acetate copolymers, vinyl chloride polymers, vinylidene chloride polymers, vinyl chloride-vinylidene copolymers, acrylo-nitrile copolymers, acrylic emulsions, styrene-butadiene latexes, elastomeric latex emulsions, ethylene-acrylic copolymers or combinations thereof. Exemplary materials for use as dry strength additives include those disclosed in U.S. Pat. Nos. 3,556,932, 3,556,933, 4,035,229, 4,129,722, 4,217,425, 5,085,736, 5,320,711, 5,674,362, 5,723,022, 6,224,174, 6,245,874, 6,749,721, 7,488,403, 7,589,153, 7,828,934, 7,897013, 4,818,341, 4,940,514, 4,957,977, 6,616,807, 7,902,312, and 7,922,867 all of which are herein incorporated by reference in their entirety.

After formation in the forming section 110, the partially dewatered web is transferred to the drying section 112. Within the drying section 112, the tissue may be dried using through air drying processes which involve the use of a structured fabric. In an exemplary embodiment, the tissue is dried to a humidity of about 7 to 20% using a through air drier manufactured by Valmet Corporation, of Espoo, Finland. In another exemplary embodiment, two or more through air drying stages are used in series. However, it should be emphasized that this is only one of various methods of manufacturing an absorbent structure to be used in manufacturing the laminate of the present invention.

In an exemplary embodiment, the tissue of the present invention is patterned during the through air drying process using a TAD fabric. FIG. 2 shows a TAD fabric, generally designated by reference number 1000, that may be used in a TAD drying process according to an exemplary embodiment of the present invention. The TAD fabric 1000 has the following attributes:

Round warp yarn in the machine direction with a diameter in the range of 0.35 mm to 0.45 mm or flat rectangular warp yarn with a range of 0.29 mm to 0.39 mm height by 0.35 mm to 0.52 mm width;

Round weft yarn in the cross-machine direction with a diameter in the range of 0.40 mm to 0.60 mm;

A weave pattern with the warp yarn passing over three consecutive weft yarns, then under three subsequent weft yarns, over the subsequent weft yarn, under the subsequent weft yarn, and then repeating the entire sequence over again throughout the fabric (8-shed weave pattern 3×3×1×1); and

The mesh (warp filaments per cross direction distance) is 16 filaments per centimeter or less with a count (weft filaments per machine direction distance) of 11 filaments per centimeter or less.

The use of this TAD fabric results in production of an absorbent structure with surface attributes of Valley Volume (Svo) greater than 11 microns and Pit density (pockets per sq.cm) greater than 25 and with multiple and varied pits or pockets. The large Valley Volume coupled with high pit density provide for enhanced absorbency without the need for excessive basis weight.

After the through air drying stage, the absorbent structure in accordance with exemplary embodiments of the present invention may be further dried in a second phase using a Yankee drying drum. In an exemplary embodiment, a creping adhesive is applied to the drum prior to the absorbent structure contacting the drum. The absorbent structure adheres to the drum and is removed using a wear resistant coated creping blade with a creping shelf of 0.5 mm or less. The creping doctor set up angle is preferably 10 to 35 degrees, while the blade bevel is preferably 55 to 80 degrees. To further illustrate the creping process, FIG. 3 shows a conventional art creping blade application wherein a creping blade 1 is pressed against a steam heated drum 3 in order to crepe a tissue web 2. The blade may be provided with a wear resistant material 4 at the blade tip. The distance of the creping shelf 15 is the same as the thickness of the creping blade 14. In comparison, as shown in FIG. 4, in accordance with exemplary embodiments of the creping process used for the invention, the distance of the creping shelf 15 has been reduced to 0.5 mm or less by beveling the non-contacting face of the blade 12. The angle of the bevel b is selected to obtain the desired creping shelf distance. Without being bound by theory, it has been discovered that distance of the creping shelf can influence the properties of the absorbent structure including tensile, bulk, and softness since the distance of the creping shelf directly influences the contact time between the blade and web and thus the forces imparted to the web by the blade. In an exemplary embodiment, a 25 degree blade set up angle (c), which is measured from a normal line at the contact point between the blade tip and the drum to the face of the creping blade 5, a wear resistant coated tip blade with an 80 degree blade bevel (d), and a 0.5 mm creping shelf distance 15 is utilized.

The wear resistant material is suitably a ceramic material, a cermet material, or a carbide material. For example, the wear resistant material may be selected from metal oxides, ceramic materials, silicates, carbides, borides, nitrides, and mixtures thereof. Particular examples of suitable wear resistant materials are alumina, chromia, zirconia, tungsten carbide, chromium carbide, zirconium carbide, tantalum carbide, titanium carbide, and mixtures thereof. The wear-resistant material may be applied by thermal spraying, physical vapor deposition, or chemical vapor deposition.

The tissue may then be calendered in a subsequent stage within the calendar section 114. According to an exemplary embodiment, calendaring may be accomplished using a number of calendar rolls (not shown) that deliver a calendering pressure in the range of 0-100 pounds per linear inch (PLI). In general, increased calendering pressure is associated with reduced caliper and a smoother tissue surface.

According to an exemplary embodiment of the invention, a ceramic coated creping blade is used to remove the absorbent structure from the Yankee drying drum. Ceramic coated creping blades result in reduced adhesive build up and aid in achieving higher run speeds. Without being bound by theory, it is believed that the ceramic coating of the creping blades provides a less adhesive surface than metal creping blades and is more resistant to edge wear that can lead to localized spots of adhesive accumulation. The ceramic creping blades allow for a greater amount of creping adhesive to be used which in turn provides improved sheet integrity and faster run speeds.

In addition to the use of wet end additives, the absorbent structure in accordance with exemplary embodiments of the present invention may also be treated with topical or surface deposited additives. Examples of surface deposited additives include softeners for increasing fiber softness and skin lotions. Examples of topical softeners include but are not limited to quaternary ammonium compounds, including, but not limited to, the dialkyldimethylammonium salts (e.g. ditallowdimethylammonium chloride, ditallowdimethylammonium methyl sulfate, di(hydrogenated tallow)dimethyl ammonium chloride, etc.). Another class of chemical softening agents include the organo-reactive polydimethyl siloxane ingredients, including amino functional polydimethyl siloxane, zinc stearate, aluminum stearate, sodium stearate, calcium stearate, magnesium stearate, spermaceti, and steryl oil.

To enhance the strength and absorbency of the absorbent structure, multiple plies are laminated together using, for example, a heated adhesive, as described below with respect to FIG. 5. The adhesive mixture is preferably water soluble and includes a mixture of one or more adhesives, one or more water soluble cationic resins and water. The one or more adhesives are present in an amount of 1% to 10% by weight of the mixture and may be polyvinyl alcohol, polyvinyl acetate, starch based resins and/or mixtures thereof. A water soluble cationic resin may be present in an amount of up to 10% by weight of the mixture and may include polyamide-epichlorohydrin resins, glyoxalated polyacrylamide resins, polyethyleneimine resins, polyethylenimine resins, and/or mixtures thereof. The remainder of the mixture is composed of water.

FIG. 5 shows an apparatus for manufacturing a laminate of two plies of a structured paper towel or tissue that are joined to each other, with the Yankee side surface of each ply facing the exterior of the laminated structure, in accordance with an exemplary embodiment of the present invention. The process illustrated in FIG. 5 is referred to as dynamic embossment knock out (DEKO) embossing. As shown, two webs 200, 201 of single ply towel which may be manufactured, for example, according to the methods described herein are plied together with only one web being embossed. A first web 200 is fed through a nip 202A formed by rubber covered pressure roll 203 and embossing roll 204 (also known as a patterned roll). The embossing roll 204 which rotates in the illustrated direction, impresses an embossment pattern onto the web 200 as it passes through the nip between emboss roll 204 and pressure roll 203. A second web 201 is fed across two idler rolls 205 and joins with web 200 at the nip between the embossing roll 204 and marrying roll 214. The idlers rolls can be driven. Alternatively, the emboss section may not have idler rolls, in which case the second web would travel directly to the nip between the embossing roll 204 and marrying roll 214.

After being embossed, the top ply may have a plurality of embossments protruding outwardly from the plane of the ply towards the adjacent ply. The emboss roll 204 has embossing tips or embossing knobs that extend radially outward from the rolls to make the embossments. In the illustrated embodiment, embossing is performed by the crests of the embossing knobs applying pressure onto the rubber pressure roll and compressing and deflecting web 200 into the pressure roll 203 and thereby imparting the imprint of the embossments into the paper web.

An adhesive applicator roll 212 is positioned upstream of emboss roll 204 and is aligned in an axially parallel arrangement with the emboss roll. The heated adhesive is fed from an adhesive tank 207 via a conduit 210 to applicator roll 212. The applicator roll 212 transfers heated adhesive to an interior side of embossed ply 200 to adhere the at least two plies 200, 201 together, wherein the interior side is the side of ply 200 that comes into a face-to-face relationship with ply 201 for lamination. The adhesive is applied to the ply at the crests of the embossing knobs on embossing roll 204. In a preferred exemplary embodiment, adhesive is applied only to the tips of the embossments formed in the ply 200.

Notably, in exemplary embodiments of the present invention, the adhesive is heated and maintained at a desired temperature utilizing, in embodiments, the adhesive tank 207, which is an insulated stainless steel tank that may have heating elements 208 that are substantially uniformly distributed throughout the interior heating surface. In this manner, a large amount of surface area may be heated relatively uniformly. Generally, an adjustable thermostat may be used to control the temperature of the adhesive tank 207. It has been found advantageous to maintain the temperature of the adhesive at between approximately 32 degrees C. (90 degrees F.) to 66 degrees C. (150 degrees F.), and preferably to around 49 degrees C. (120 degrees F.). In addition, in embodiments, the tank has an agitator 209 to ensure proper mixing and heat transfer.

After the application of the embossments and the adhesive, a marrying roll 214 is used to apply pressure for lamination. The marrying roll 214 forms a nip with the embossing roll 204. The marrying roll 214 is generally needed to apply pressure to the two webs to allow the adhesive on the crests of the embossments on web 200 to contact and adhere to and laminate to web 201.

The specific pattern that is embossed on the absorbent products is significant for achieving the enhanced scrubbing resistance of the present invention. In particular, it has been found that the embossed area on the top ply should cover between approximately 5 to 15% of the surface area. Moreover, the size of each embossment should be between approximately 0.04 to 0.08 square centimeters. The depth of the embossment should be within the range of between approximately 0.127 and 0.43 centimeters (0.050 and 0.170 inches) in depth.

The emboss pattern used is also important to provide adequate area for bonding the laminate while limiting absorbency loss, as the laminated areas will absorb less than the non-laminated areas. In a preferred exemplary embodiment, the embossed area on any ply should be in the range of 5% to 15%. The size of each embossment is preferably in the range of 0.04 to 0.08 square centimeters. The depth of each embossment is preferably in the range of 0.05 and 0.170 inches.

The combination of the structuring fabric and lamination method provides a disposable towel product with high levels of absorbency at low levels of basis weight with good strength and performance.

Ball Burst Testing

The Ball Burst of a 2-ply tissue web was determined using a Tissue Softness Analyzer (TSA), available from Emtec Electronic GmbH of Leipzig, Germany using a ball burst head and holder. A punch was used to cut out five 100 cm² round samples from the web. One of the samples was loaded into the TSA, with the embossed surface facing down, over the holder and held into place using the ring. The ball burst algorithm was selected from the list of available softness testing algorithms displayed by the TSA. The ball burst head was then pushed by the TSA through the sample until the web ruptured and calculated the grams force required for the rupture to occur. The test process was repeated for the remaining samples and the results for all the samples were averaged.

Stretch & MD, CD, and Wet CD Tensile Strength Testing

An Instron 3343 tensile tester, manufactured by Instron of Norwood, Mass., with a 100N load cell and 25.4 mm rubber coated jaw faces, was used for tensile strength measurement. Prior to measurement, the Instron 3343 tensile tester was calibrated using Operator's Guide M10-16279-EM Revision D. After calibration, 8 strips of 2-ply product, each 2.54 cm by 10.16 cm (one inch by four inches), were provided as samples for each test. When testing MD (Material Direction) tensile strength, the strips were cut in the MD direction. When testing CD (Cross Direction) tensile strength, the strips were cut in the CD direction. One of the sample strips was placed in between the upper jaw faces and clamp, and then between the lower jaw faces and clamped with a gap of 5.08 cm (2 inches) between the clamps. A test was run on the sample strip to obtain tensile strength and stretch. The test procedure was repeated until all the samples were tested. The values obtained for the eight sample strips were averaged to determine the tensile strength of the tissue. When testing CD wet tensile, the strips were placed in an oven at 105 degrees Celsius for 5 minutes and saturated with 75 microliters of deionized water at the center of the strip across the entire cross direction immediately prior to pulling the sample.

Basis Weight

Using a dye and press, six 76.2 mm by 76.2 mm square samples were cut from a 2-ply product being careful to avoid any web perforations. The samples were placed in an oven at 105 deg C. for 5 minutes before being weighed on an analytical balance to the fourth decimal point. The weight of the sample in grams was divided by (0.0762 m)² to determine the basis weight in grams/m².

Caliper Testing

A Thwing-Albert ProGage 100 Thickness Tester, manufactured by Thwing Albert of West Berlin, N.J. was used for the caliper test. The Thickness Tester was used with a 2 inch diameter pressure foot with a preset loading of 0.93 grams/square inch. Eight 100 mm×100 mm square samples were cut from a 2-ply product. The samples were then tested individually and the results were averaged to obtain a caliper result for the base sheet.

Softness Testing

Softness of a 2-ply tissue web was determined using a Tissue Softness Analyzer (TSA), available from Emtec Electronic GmbH of Leipzig, Germany. The TSA comprises a rotor with vertical blades which rotate on the test piece to apply a defined contact pressure. Contact between the vertical blades and the test piece creates vibrations which are sensed by a vibration sensor. The sensor then transmits a signal to a PC for processing and display. The frequency analysis in the range of approximately 200 to 1000 Hz represents the surface smoothness or texture of the test piece and is referred to as the TS750 value. A further peak in the frequency range between 6 and 7 kHz represents the bulk softness of the test piece and is referred to as the TS7 value. Both TS7 and TS750 values are expressed as dB V² rms. The stiffness of the sample is also calculated as the device measures deformation of the sample under a defined load. The stiffness value (D) is expressed as mm/N. The device also calculates a Hand Feel (HF) number with the value corresponding to a softness as perceived when someone touches a tissue sample by hand (the higher the HF number, the higher the softness). The HF number is a combination of the TS750, TS7, and stiffness of the sample measured by the TSA and calculated using an algorithm which also requires the caliper and basis weight of the sample. Different algorithms can be selected for different facial, toilet, and towel paper products. Before testing, a calibration check should be performed using “TSA Leaflet Collection No. 9” (dated 2016 May 10) available from Emtec. If the calibration check demonstrates a calibration is necessary, “TSA Leaflet Collection No. 10” is followed for the calibration procedure available from Emtec dated 2015 Sep. 9.

A punch was used to cut out five 100 cm² round samples from the web. One of the samples was loaded into the TSA, clamped into place (outward facing or embossed ply facing upward), and the TPII algorithm was selected from the list of available softness testing algorithms displayed by the TSA. After inputting parameters for the sample (including caliper and basis weight), the TSA measurement program was run. The test process was repeated for the remaining samples and the results for all the samples were averaged and the average HF number recorded.

Valley Volume (Svo) and Pit Density

Valley Volume is a parameter that measures valley volume per unit area in a sample's 3D data set through the use of its material ratio curve, shown in FIG. 6. The most horizontal line in a 40% wide region of the material ratio curve is recognized and a straight line is drawn that extends the whole length of the curve. The region shown in gray below the horizontal line is considered the valley area, but when using a 3D data set, it is the valley volume.

Svo can be further understood by referencing ISO 25178-2, the contents of which are incorporated herein by reference in their entirety.

Pit Density—measures the number of pockets in the sample that do not travel the entire x or y axis in the given field of view. These pockets, or pits, are totally contained or framed as shown in the far right window of FIG. 7. The objective of this test method is to eliminate confusion when trying to count openings in the paper. The openings are irregular shaped and have different depths. The goal of the Pit Density test is to count the number of openings regardless of shape.

Images used to calculate the Valley Volume (Svo) and Pit Density were acquired using a Keyence Model VR-3200 G2 3D Macroscope equipped with motorized XY stage, VR-3000K controller, VR-H2VE version 2.2.0.89 Viewer software, and VR-H2AE Analyzer software. After following calibration procedures, as outlined by the Keyence equipment manual from 2016, the instrument was configured for 25× magnification. The following was selected on the viewer software: “Expert mode” for viewer capture method, and “normal” capture image type for Camera settings. For Measurement settings: “Glare removal” mode was selected with “both sides” measurement direction, Adjust brightness for measurement set to “Auto,” and Display missing and saturated data turned “ON.” This results in a “3D surface data set” which is approximately 12.1 mm (X direction) by 9.1 mm (Y direction) with a pixel size of approximately 7.9 microns.

On paper towels, the top surface of the top ply is the surface of interest, avoiding any and all emboss points if possible. Embossments are not representative of the majority of the surface and should be avoided during the “3D surface data set” acquisition. A representative paper towel sheet was torn from the center of a roll and held in place using weights. When tearing the sheet from the roll, care was taken to not alter the topographic features of the sample. The machine direction (MD) of the sample was placed in the Y axis (front to back on the stage as seen from operator perspective in front of the system) while the cross direction (CD) was placed in the X axis (left to right on the stage as seen from operator perspective in front of the system). Care was taken to ensure no creases or folds were present in the sample and the sample was not under any MD or CD directional stress. The image was autofocused prior to capturing the “3D surface data set”. Ten of these “3D surface data sets” were collected for each sample.

“3D surface data sets” were exported from the analyzer software with image type “Height” and the “No Skip” option selected. These “3D surface data sets” were analyzed with OmniSurf3D (v1.01.052) software, available from Digital Metrology Solutions, Inc. of Columbus, Ind., USA for parameter calculations.

The OmniSurf3D settings were set as follows:

Preprocessing: Alignment—Auto-trim to Valid, Edge Discarding—Use all data,

Outlier Removal—None, Missing Data Filling—Linear Fill, Data Inversion—None, Transform, Rotate—0,

Geometry: Reference Geometry—Polynomial, X-order=4, Y-order=4,

Filtering: Short Wavelength Limitation—Gaussian/0.80000 mm/Sync X&Y,

Long Wavelength Limitation-Gaussian/8.00000 mm/Sync X&Y, Post-Filter Edge Discarding—None

The Pre-processing settings are shown in FIG. 8. The Geometry Settings are shown in FIG. 9. The Filtering settings are shown in FIG. 10.

The settings described above were chosen to remove underlying curvatures in the samples. The desired exported file from the Keyence software was opened in the Omnisurf 3D software. In the “analysis” menu, “parameters” was selected, and Svo was chosen. The user clicked “OK” and the Svo value was recorded. For Pit Density, the “Pit/Porosity Analysis” tool was selected in the “Tools” menu. “Height Above Meanline” was chosen and the height was set to 0. The user clicked “Apply” and the Pit Density was recorded.

Absorbency Testing

An M/K GATS (Gravimetric Absorption Testing System), manufactured by M/K Systems, Inc., of Peabody, Mass., USA was used to test absorbency using MK Systems GATS Manual from Mar. 30, 2016. Absorbency is reported as grams of water absorbed per gram of absorbent product. The following steps were followed during the absorbency testing procedure:

Turn on the computer and the GATS machine. The main power switch for the GATS is located on the left side of the front of the machine and a red light will be illuminated when power is on. Ensure the balance is on. A balance should not be used to measure masses for a least 15 minutes from the time it is turned on. Open the computer program by clicking on the “MK GATS” icon and click “Connect” once the program has loaded. If there are connectivity issues, make sure that the ports for the GATS and balance are correct, the GATS being attached to “COM7” and the balance being attached to “COMB”. These can be seen in Full Operational Mode. The upper reservoir of the TAS needs to be filled with Deionized water. The Velmex slide level for the wetting stage needs to be set at 4.5 cm. If the slide is not at the proper level, movement of it can only be accomplished in Full Operational Mode. Click the “Direct Mode” check box located in the top left of the screen to take the system out of Direct Mode and put into Full Operational Mode. The level of the wetting stage is adjusted in the third window down on the left side of the software screen. To move the slide up or down 1 cm at a time, the button for “1 cm up” and “1 cm down” can be used. If a millimeter adjustment is needed, press and hold the shift key while toggling the “1 cm up” or “1 cm down” icons. This will move the wetting stage 1 mm at a time. Click the “Test Options” Icon and ensure the following set-points are inputted: “Dip Start” selected with 10.0 mm inputted under “Absorption”, “Total Weight change (g)” selected with 0.1 inputted under “Start At”, Rate (g) selected with 0.05 inputted per (sec) 5 under “End At” on the left hand side of the screen, “Number of Raises” 1 inputted and regular raises (mm) 10 inputted under “Desorption”, Rate (g) selected with −0.03 inputted per 5 sec under “End At” on the right hand side of the screen. These selections are also shown in FIG. 8. The water level in the primary reservoir needs to be filled to the operational level before any series of testing. This involves the reservoir and water contained in it to be set to 580 grams total mass. Click on the “Setup” icon in the box located in the top left of the screen. The reservoir will need to be lifted to allow the balance to tare or zero itself. The feed and draw tubes for the system are located on the side and extend into the reservoir. Prior to lifting the reservoir, ensure that the top hatch on the balance is open to keep from damaging the top of the balance or the elevated platform that the sample is weighed on. Open the side door of the balance to lift the reservoir. Once the balance reading is stable a message will appear to place the reservoir again. Ensure that the reservoir doesn't make contact with the walls of the balance. Close the side door of the balance. The reservoir will need to be filled to obtain the mass of 580 g. Once the reservoir is full, the system will be ready for testing. The system is now ready to test. Obtain a minimum number of four 113 mm diameter circular samples. Three will be tested with one extra available. Enter the pertinent sample information in the “Enter Material ID.” section of the software. The software will automatically date and number the samples as completed with any used entered data in the center of the file name. Click the “Run Test” icon. The balance will automatically zero itself. Place the pre-cut sample on the elevated platform, making sure the sample isn't in contact with the balance lid. Once the balance load is stabilized, click “Weigh”. Move the sample to the wetting stage, centered with the emboss facing down. Ensure the sample doesn't touch the sides and place the cover on the sample. Click “Wet the Sample”. The wetting stage will drop the preset distance to initiate absorption. The absorption will end when the rate of absorption is less than 0.05 grams/5 seconds. When absorption stops, the wetting stage will rise to conduct desorption. Data for desorption isn't recorded for tested sample. Remove the saturated sample and dry the wetting stage prior to the next test. Once the test is complete, the system will automatically refill the reservoir. Record the data generated for this sample. The data that is traced for each sample is the dry weight of the sample (in grams), the normalized total absorption of the sample reflected in grams of water/gram of product, and the normalized absorption rate in grams of water per second. Repeat procedure for the three samples and report the average total absorbency.

The towel of the present invention exhibits a unique Valley Volume Svo of greater than 11 microns and Pit density (pockets per sq cm.) of greater than 25 with multiple and varied pits/pockets.

The following example illustrates advantages of the present invention.

Example 1

Paper towel made on a wet-laid asset with a three layer headbox was produced using the through air drying method. A TAD fabric weave pattern was used with the warp yarn passing over three consecutive weft yarns, then under three subsequent weft yarns, over the subsequent weft yarn, under the subsequent weft yarn, and then repeating the entire sequence over again throughout the fabric was utilized. The fabric had a 16 filaments/cm Mesh and 11 filaments/cm Count, a 0.40 mm diameter round warp monofilament, a 0.55 mm diameter round weft monofilament, a 1.17 mm caliper, with a 620 cfm and a knuckle surface that was sanded to impart 15% contact area with the Yankee dryer. The flow to each layer of the headbox was about 33% of the total sheet. The three layers of the finished tissue from top to bottom were labeled as air, core and dry. The air layer is the outer layer that is placed on the TAD fabric, the dry layer is the outer layer that is closest to the surface of the Yankee dryer and the core is the center section of the tissue. The tissue was produced with 50% NBSK and 50% eucalyptus in the Yankee layer with 80% NB SK, 20% eucalyptus in the core and air layer. Polyamine polyamide-epichlorohydrin resin at 8.0 kg/ton (dry basis) and 3.5 kg/ton (dry basis) of anionic polyacrylamide were added to each of the three layers to generate permanent wet strength. The NBSK was refined separately before blending into the layers using 80 kwh/ton on one conical refiner. The Yankee and TAD section speed was 1350 m/min running 12% slower than the forming section. The Reel section was additionally running 1% slower than the Yankee. The towel was then plied together using the method described herein using a steel emboss roll with the pattern shown in FIG. 13 and 7% polyvinyl alcohol based adhesive heated to 120 deg F. A rolled 2-ply product was produced with 146 sheets and a roll diameter of 150 mm, with each sheet having a length of 6.0 inches and a width of 11 inches. The 2-ply tissue product had the following product attributes: Basis Weight 39.8 g/m², Caliper 0.843 mm, MD tensile of 410 N/m, CD tensile of 388 N/m, a ball burst of 898 grams force, an MD stretch of 17.9%, a CD stretch of 8.8%, a CD wet tensile of 113 N/m, an absorbency of 18.3 g/g, and a TSA softness of 46.6. The Svo value was 14.3 microns, with a Pit Density of 32.3 pockets per sq cm. FIG. 11 shows an image of the surface of the disposable paper towel produced in this Example magnified at 20 times.

Comparative Example

Paper towel made on a wet-laid asset with a three layer headbox was produced using the through air dried method. A TAD fabric design named Prolux 593 supplied by Albany (216 Airport Drive Rochester, N.H. 03867 USA Tel: +1.603.330.5850) was utilized. The fabric had a 45 yarns/inch Mesh and 27 yarns/inch Count, a 0.35 mm warp monofilament, a 0.55 mm weft monofilament, a 1.89 mm caliper, with a 670 cfm and a knuckle surface that was sanded to impart 15% contact area with the Yankee dryer. The flow to each layer of the headbox was about 33% of the total sheet. The three layers of the finished tissue from top to bottom were labeled as air, core and dry. The air layer is the outer layer that is placed on the TAD fabric, the dry layer is the outer layer that is closest to the surface of the Yankee dryer and the core is the center section of the tissue. The tissue was produced with 50% NBSK and 50% eucalyptus in the Yankee layer with 80% NB SK, 20% eucalyptus in the core and air layer. Polyamine polyamide-epichlorohydrin resin at 12.0 kg/ton (dry basis) and 4.0 kg/ton (dry basis) of carboxymethylcellulose were added to each of the three layers to generate permanent wet strength. Additionally, 1.5 kg/ton of polyvinyl amine was added to each layer to aid in fiber retention with 2.0 kg of amphoteric starch for additional strength generation. The NBSK was refined separately before blending into the layers using 100 kwh/ton on one conical refiner. The Yankee and TAD section speed was 1200 m/min running 17% slower than the forming section. The Reel section was additionally running 1% faster than the Yankee. The towel was then plied together using the method described herein using a steel emboss roll with the pattern shown in FIG. 13 and 7% polyvinyl alcohol based adhesive heated to 120 deg F. A rolled 2-ply product was produced with 146 sheets and a roll diameter of 147 mm, with each sheet having a length of 6.0 inches and a width of 11 inches. The 2-ply tissue product had the following product attributes: Basis Weight 39.09 g/m², Caliper 0.880 mm, MD tensile of 429 N/m, CD tensile of 491 N/m, a ball burst of 1098 grams force, an MD stretch of 21.4%, a CD stretch of 13.3%, a CD wet tensile of 146 N/m, an absorbency of 15.9 g/g, and a TSA softness of 44.4. Svo value was 6.9 microns, with a Pit Density of 43 pockets per sq cm.

FIG. 12 shows the surface parameters and physical properties of the Comparative Example and various commercially available disposable towel products compared to Example 1.

Now that embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be construed broadly and not limited by the foregoing specification. 

The invention claimed is:
 1. An absorbent product comprising a laminate of at least two plies of structured tissue with each ply being multi-layered, wherein the absorbent product has a measured Valley Volume parameter greater than 11 microns, a Pit Density of greater than 25 pockets per sq. cm, and a basis weight of less than 45 grams per square meter.
 2. The absorbent product of claim 1, wherein the absorbent product has an absorbency of greater than 16.0 grams of water absorbed per gram of absorbent product.
 3. The absorbent product of claim 1, wherein the absorbent product has a basis weight of less than 43 grams per square meter.
 4. The absorbent product of claim 1, wherein the absorbent product is produced using a wet laid structured tissue process.
 5. The absorbent product of claim 1, wherein at least one of the at least two plies comprises cellulosic-based fibers.
 6. The absorbent product of claim 5, wherein the cellulosic-based fibers are selected from the group consisting of wood pulp, cannabis, cotton, regenerated or spun cellulose, jute, flax, ramie, bagasse, kenaf fibers and combinations thereof.
 7. The absorbent product of claim 5, wherein at least one of the at least two plies comprises synthetic fibers.
 8. The absorbent product of claim 7, wherein the synthetic fibers are made from a polymer selected from the group consisting of polyolefin, polyester, polypropylene and polylactic acid.
 9. The absorbent product of claim 5, wherein the absorbent product comprises both synthetic and cellulosic based polymers.
 10. The absorbent product of claim 1, wherein at least one of the two plies comprises synthetic fibers.
 11. The absorbent product of claim 10, wherein the synthetic fibers are made from a polymer selected from the group consisting of polyolefin, polyester, polypropylene and polylactic acid.
 12. The absorbent product of claim 1, wherein each of the at least two plies is embossed and the at least two plies are adhered together.
 13. The absorbent product of claim 12, wherein the at least two plies are adhered together with a water soluble adhesive mixture comprised of polyvinyl alcohol, polyvinyl acetate, starch based resins or mixtures thereof.
 14. The absorbent product of claim 12, wherein the water soluble adhesive is applied to at least one ply of the at least two plies at a temperature within a range of 32 degrees C. to 66 degrees C.
 15. The absorbent product of claim 12, wherein the water soluble adhesive mixture further comprises a water soluble cationic resin selected from the group consisting of polyamide-epichlorohydrin resins, glyoxalated polyacrylamide resins, polyethyleneimine resins, polyethylenimine resins, and mixtures thereof.
 16. The absorbent product of claim 12, wherein each of the at least two plies comprises an embossed area, wherein the embossed area occupies between approximately 5 to 15% of the total surface area of a surface of the ply.
 17. The absorbent product of claim 12, wherein each of the at least two plies comprises an embossed area having a surface, wherein a depth of embossment of the surface is between approximately 0.28 and 0.43 centimeters.
 18. The absorbent product of claim 12, wherein each of the at least two plies comprises an embossed area having a surface, wherein each embossment of the surface is between approximately 0.04 and 0.08 square centimeters in size.
 19. The absorbent product of claim 1, wherein the absorbent product is one of a paper towel, a disposable towel or wipe, a bath or facial tissue, or a nonwoven product.
 20. The absorbent product of claim 1, wherein the absorbent product has an absorbency of greater than 18.0 grams of water absorbed per gram of absorbent product.
 21. The absorbent product of claim 1, wherein the absorbent product has a basis weight of less than 40 grams per square meter. 